Volume test for volume_extension:volume_actions:upload_public

This commit adds a test for testing the policy action:
volume_extension:volume_actions:upload_public.

Specifically:
  - adds test for volume_extension:volume_actions:upload_public
    whose minimum microversion is 3.10 [0]
  - changes the image_client for related test for test_volume_upload
    to use the admin image client for waiting for status change
  - tags this test and related test_volume_upload test as slow
    since they both take 20 secs or more to complete

[0] https://github.com/openstack/cinder/blob/a98a16a658244814c079b01a0c4d05e2a1deca43/cinder/api/contrib/volume_actions.py#L272

Change-Id: I2d69b48202b4dc6b4ef4adcb5bf2388353ccbd9d
diff --git a/releasenotes/notes/volume-upload-public-test-f8e741a838ae7607.yaml b/releasenotes/notes/volume-upload-public-test-f8e741a838ae7607.yaml
new file mode 100644
index 0000000..c8c0ecd
--- /dev/null
+++ b/releasenotes/notes/volume-upload-public-test-f8e741a838ae7607.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add RBAC test to provide coverage for the following cinder policy:
+    "volume_extension:volume_actions:upload_public".